FIG. 4 shows a configuration of a conventional refrigeration cycle device described in patent document 1.
A hermetic type compressor 801 includes a main compressing element 802 and an auxiliary compressing element 803. A main compressing element discharging pipe 804 and an auxiliary compressing element discharging pipe 805 merge with each other and become a high pressure gas pipe 806. The refrigeration cycle device includes a condenser 807, a high pressure liquid pipe 808, a decompressor 809, an evaporator 810 and a low pressure gas pipe 811. The low pressure gas pipe 811 connects the compressor 801 and the evaporator 810 to each other. The low pressure gas pipe 811 bifurcates into a main compressing element suction pipe 812 and an auxiliary compressing element suction pipe 813. The auxiliary compressing element discharging pipe 805 is provided with a high pressure-side check valve 814. The main compressing element suction pipe 812 is provided with a low pressure-side check valve 815. The bypass pipe 816 connects, to each other, the low pressure-side check valve 815 on the side of the main compressing element 802 and the auxiliary compressing element 803 on the side of the high pressure-side check valve 814. The bypass pipe 816 is provided with a bypass control two-way valve 817 for flowing a refrigerant when capacity is controlled.
Operation of a refrigeration cycle at the time of full operation (at the time of the high capacity mode of compressor) in which capacity is not controlled will be described.
At the time of full operation, the bypass control two-way valve 817 is closed. The compressor 801 is operated, refrigerants which respectively come out from the compressing elements 802 and 803 respectively pass through the discharging pipes 804 and 805 and merge with each other in the high pressure gas pipe 806, and flow to the condenser 807, the decompressor 809 and the evaporator 810. The refrigerant which comes out from the evaporator 810 passes through the low pressure gas pipe 811, a portion of the refrigerant is sucked into the main compressing element 802 through the low pressure-side check valve 815 and the main compressing element suction pipe 812, and another portion of the refrigerant is sucked into the auxiliary compressing element 803 through the auxiliary compressing element suction pipe 813.
Operation of the refrigeration cycle when a load becomes small and capacity is controlled (at the time of low capacity mode of compressor) will be described.
When capacity is controlled, the bypass control two-way valve 817 is opened. The compressor 801 is operated, and a refrigerant which comes out from the auxiliary compressing element 803 passes through the bypass pipe 816 and the bypass control two-way valve 817 and is guided into the main compressing element suction pipe 812. At this time, the auxiliary compressing element suction pipe 813 becomes a suction side of the auxiliary compressing element 803, and the main compressing element suction pipe 812 becomes a discharge side of the auxiliary compressing element 803. Therefore, since a pressure in the main compressing element suction pipe 812 becomes higher than that in the auxiliary compressing element suction pipe 813, the low pressure-side check valve 815 is brought into a closed state. Therefore, refrigerant gas does not flow from the low pressure gas pipe 811 to the main compressing element suction pipe 812. Only a refrigerant which passes through the bypass pipe 816 and is guided into the main compressing element suction pipe 812 is sucked into the main compressing element 802.
A refrigerant flows from the auxiliary compressing element 803 into the main compressing element 802, the refrigerant is discharged from the main compressing element discharging pipe 804, and flows to the high pressure gas pipe 806, the condenser 807, the decompressor 809 and the evaporator 810 in this order, and returns from the auxiliary compressing element suction pipe 813 to the auxiliary compressing element 803.
The bypass pipe 816 becomes the suction side of the main compressing element 802 and the high pressure gas pipe 806 becomes the discharge side of the main compressing element 802. Therefore, a pressure in the high pressure gas pipe 806 becomes higher than that in the bypass pipe 816. Hence, the high pressure-side check valve 814 is brought into a closed state. Therefore, a refrigerant which comes out from the auxiliary compressing element 803 does not flow to the auxiliary compressing element discharging pipe 805.
As described above, when capacity is controlled (at the time of low capacity mode of compressor), the auxiliary compressing element 803 and the main compressing element 802 are connected to each other in series. Usually, when the two compressing elements 802 and 803 are connected to each other in series, it is preferable from the aspect of efficiency that theoretical suction capacity of a high pressure-side compressing element (compressing element corresponding to main compressing element 802 in FIG. 4) is set smaller than theoretical suction capacity of a low pressure-side compressing element (compressing element corresponding to auxiliary compressing element 803 in FIG. 4), and compressing operation is carried out in two stages so that a compression ratio on the low pressure-side and a compression ratio on the high pressure-side become equal to each other.
When it is desired to set capacity control ratio large, i.e., it is desired to set minimum ability small, if theoretical suction capacity on the low pressure-side is set smaller than theoretical suction capacity on the high pressure-side, since compressor ability in serial operation of the compressing element 802 is determined by theoretical suction capacity on the low pressure-side, its object is achieved. In the case of the two stage compressor, it is general that theoretical suction capacities of the main compressing element 802 and the auxiliary compressing element 803 are set different from each other.